A. Field of the Invention
This invention relates to the field of loading fluid into trailers and in particular to control of such loading from a fixed control system.
B. Background Art
When loading volatile liquids, such as cryogenic liquids, into sealed tanks inside trailers, it is difficult to assure safety and accuracy. Conventionally, a differential pressure meter is provided at the rear of the trailer. This meter was used to obtain an indication of the level of the liquid within the tank. However, trailer-mounted analog liquid gauges are inherently inaccurate, having an accuracy of only plus or minus one percent when new. Furthermore, because this differential pressure meter is permanently attached to the trailer, it is subject to a great deal of vibration and other abuse which causes the accuracy to deteriorate to plus or minus five percent or worse after a period of use.
With respect to safety, it was required that the person filling the trailer be present where the differential pressure meter is mounted at the rear of the trailer in order to observe the meter. This location is in proximity to the coupling between the flexible filling hose and the intake connection. Thus, any accidental spilling of the liquid, blow-off of excess pressure, or other type of accident exposed this person to danger, particularly if the fluid or its vapors were toxic. In order to control filling manual opening and closing of a valve in the supply pipe has been required. This resulted in inaccuracy because manual closing of the valves could take as long as three to five minutes.
The vibration due to driving and road dust and dirt causes linkages within the differential pressure gauge to stick. Additionally, the environment within the rear of the truck where the differential pressure gauge is mounted is very severe. If the liquid stored in the tank is a cryogenic liquid, the rear is cold and foggy. These conditions combine to cause the accuracy of truck-mounted differential pressure gauges to decline to .+-.5% or worse.
A more accurate method of controlling level has been in the use of a direct acting weight scale. However, it does not eliminate the danger to the operator and it is very costly to retrofit a facility with scales.
U.S. Pat. No. 4,266,580 shows a system for loading tank cars. U.S. Pat. No. 3,618,643 (Hovant) teaches a loading bay for filling the compartments of a vehicle with liquid fuel. However, neither of these patents are considered suitable or readily adaptable for use in loading cryogenic liquids into sealed tanks because they include inserting an apparatus into the tanks being loaded.
For purposes of considering the patentability of the invention disclosed and claimed herein, a brief patentability search has been conducted. In addition to the patents mentioned above, other patents identified to be of possible interest in this search were:
______________________________________ 3,494,387 Gillies et al 3,916,961 Dilger 3,983,913 Bower 4,082,122 McGahey ______________________________________
However, none of the devices taught by the foregoing patents appears adaptable to automatic precision liquid loading of cryogenic liquids.
It is an object of the present invention to provide a system for filling sealed tanks with fluid wherrein the level of fluid may be controlled with precision.
It is an additional object of the present invention to provide a system for filling sealed tanks in trailers in which operator control functions are performed remotely from the trailer to assure operator safety.